1. Field of the Invention
The present invention relates to an optical disc device and particularly relates to an optical disc controller for performing servo control in the optical disc device.
2. Description of the Related Art
Referring to FIGS. 8 and 9, a conventional art will be described below. FIG. 8 is a block diagram showing a conventional optical disc device 400. The configuration of a driving system is mainly shown in FIG. 8. FIG. 9 shows waveforms indicating the timing of controlling constituent elements in the driving system of the optical disc device 400. The optical disc device 400 comprises a disc motor 402, an optical head 403, and a digital signal processor (hereinafter, abbreviated as DSP) 412. The disc motor 402 is loaded with an optical disc 401 and rotates the disc.
The optical head 403 includes a light source (not shown) for emitting a light beam, a converging lens 405 for converging a light beam, an actuator 407 for driving the converging lens 405, a detector 404, and an analog operational unit 408. The optical head 403 emits a light beam converged on the recording surface of the optical disc 401. The photodetector 404 mounted on the optical head 403 detects the reflected light or transmitted light of the light beam and converts the light into an electric signal. As shown in FIG. 8, the photodetector 404 is divided into areas 404a and 404c and areas 404b and 404d along the tangential direction of tracks and is divided into the areas 404a and 404b and the areas 404c and 404d along the perpendicular direction of the tracks. Namely, the detection area of the photodetector 404 is divided into four.
The converging lens 405 mounted on the optical head 403 is driven by the actuator 407 along a focusing direction, which is perpendicular to the recording surface of the optical disc 401, and the radius direction of the optical disc 401. The whole optical head 403 can be moved in the radius direction of the optical disc 401 by a traverse motor 406.
The analog operational unit 408 receives the output of the photodetector 404 and outputs an FE+ signal and an FE− signal. By computing a difference between the FE+ signal and the FE− signal, a focus error signal can be obtained which indicates a displacement between the focus of a light beam and the information recording surface. For example, when the focus error signal is obtained by the astigmatic method, the FE+ signal is generated from an added signal of the photodetectors 404a and 404d and the FE− signal is generated from an added signal of the photodetectors 404b and 404c. 
The DSP 412 operates according to an output clock of a clock output unit 423 and performs the following operations according to the output of an interrupt timer 422 shown in FIG. 9(A).
First, the DSP 412 starts, from time D1, an operation for controlling the disc motor (indicated by DM in FIG. 9(I)). The disc motor 402 outputs an FG signal according to a rotational period, and the period of the FG signal is counted by a period counter 421. According to an instruction of a system controller 424, the DSP 412 performs a digital filtering operation on a difference between the output of the period counter 421 and a disc motor rotation target RAM according to a disc motor filter coefficient set for the RAM (not shown) of the DSP 412, and the DSP 412 outputs an arithmetic result, as a control signal for driving the disc motor 402, to a PWM converter 416 at the timing of FIG. 9(M). The PWM converter 416 receives the control signal and performs pulse width modulation thereon and outputs the signal to a driving circuit 420. The driving circuit 420 performs power amplification on the received signal and supplies the signal to the traverse motor 402. Thus, control is performed so as to set the revolution speed (number of revolution) of the disc motor 402 at a predetermined value.
At this point, as shown in FIG. 9(B), an A/D converter 411 transmits an S/H signal to a sample hold circuit 409 in parallel with the above processing and the A/D converter 411 samples and holds the FE+ signal and the FE− signal at time S1. Further, as shown in FIG. 9(C), the A/D converter 411 transmits a control signal so that a selector 410 outputs the FE+ signal at time S1. As shown in FIG. 9(D), the A/D converter 411 performs A/D conversion. As shown in FIG. 9(E), the A/D converter 411 obtains an A/D converted value (FE+ converted value) by converting the FE+ signal to a digital signal. Further, A/D converter 411 transmits a control signal to the selector 410 so that the selector 410 outputs an FE− signal at time S2. As shown in FIG. 9(D), the A/D converter 411 performs A/D conversion. As shown in FIG. 9(F), the A/D converter 411 obtains an A/D converted value (FE− converted value) by converting the FE− signal into a digital signal.
As shown in FIG. 9(I), the DSP 412 starts a focus control operation (indicated by Fc in FIG. 9(I)) from time D2. The DSP 412 calculates a difference between the FE+ signal (FE+ converted value) and the FE− signal (FE− converted value) that have been converted into digital values by the A/D converter 411 and the DSP 412 obtains a focus error signal. According to an instruction of the system controller 424, the DSP 412 performs a digital filtering operation on the focus error signal according to a focus filter coefficient set for the RAM (not shown) of the DSP 412 and outputs an arithmetic result, as a control signal for driving the focusing coil of the actuator 407, to a D/A converter 413 at the timing of FIG. 9(J). The D/A converter 413 converts the output of the DSP 412 into an analog value and outputs the value to a driving circuit 417. The driving circuit 417 performs power amplification on the analog control signal and supplies the signal to the focusing coil of the actuator 407. Thus, control is performed so as to position the convergent point of a light beam on the information recording surface of the optical disc 401.
Moreover, the output of the photodetector 404 is inputted to the analog operational unit 408, and the analog operational unit 408 outputs a TE+ signal and a TE− signal. By computing a difference between the TE+ signal and the TE− signal, a tracking error signal can be obtained which indicates a displacement between the focus of a light beam and a track. For example, when the tracking error signal is obtained by the push-pull method, the TE+ signal is an added signal of signals from the photodetectors 404a and 404c and the TE− signal is an added signal of signals from the photodetectors 404b and 404d. 
The A/D converter 411 transmits a control signal to the sample hold circuit 409 so as to sample and hold the TE+ signal and the TE− signal at time S3. Further, the A/D converter 411 transmits a control signal to the selector 410 so as to output the TE+ signal at time S3. As shown in FIG. 9(G), the A/D converter 411 performs A/D conversion to obtains an A/D converted value (TE+ converted value), which is a digital signal of the TE+ signal. Moreover, the A/D converter 411 transmits a control signal to the selector 410 so as to output the TE− signal at time S4. As shown in FIG. 9(H), the A/D converter 411 performs A/D conversion to obtain an A/D converted value (TE− converted value), which is a digital signal of the TE− signal.
The DSP 412 starts a tracking control operation (indicated by Tk in FIG. 9(I)) from time D3. The DSP 412 computes a difference between the TE+ signal (TE+ converted value) and the TE− signal (TE− converted signal) that have been converted into digital values by the A/D converter 411 and the DSP 412 obtains a tracking error signal. According to the instruction of the system controller 424, the DSP 412 performs a digital filtering operation on the tracking error signal according to a tracking filter coefficient set for the RAM (not shown) of the DSP 412 and outputs an arithmetic result, as a control signal for driving the tracking coil of the actuator 407, to a D/A converter 414 at the timing of FIG. 9(K). The D/A converter 414 converts the output of the DSP 412 into an analog value and outputs the value to a driving circuit 418. The driving circuit 418 performs power amplification on the analog control signal and supplies the signal to the tracking coil of the actuator 407. Control is performed so as to position the convergent point of a light beam at the center of the tracks of the optical disc 401.
Further, the DSP 412 starts a traverse control operation (indicated by TRS in FIG. 9(I)) from time D4. According to an instruction of the system controller 424, the DSP 412 performs a digital filtering operation on the tracking error signal according to a traverse filter coefficient set for the RAM (not shown) of the DSP 412 and outputs an arithmetic result, as a control signal for driving the traverse motor 406, to a PWM converter 415 at the timing of FIG. 9(L). The PWM converter 415 receives the control signal, performs pulse width modulation thereon, and outputs the signal to a driving circuit 419. The driving circuit 419 performs power amplification on the received signal and supplies the signal to the traverse motor 406. Hence, the position of the optical head 403 is controlled so as to position the convergent point of a light beam at the center of the tracks of the disc 401.
The DSP 412 waits from time D5 indicating the completion of the traverse control operation (TRS) to time D6 indicating the subsequent output of the interrupt timer 422.
When recording and reproducing speeds are changed in the conventional optical disc device 400, the system controller 424 rewrites the disc motor rotation target RAM, the disc motor filter coefficient RAM, the focus filter coefficient RAM, and the tracking filter coefficient RAM of the DSP 412, as disclosed in, for example, Japanese Laid-Open Patent Publication No. 11-185259. Hence, recording and reproduction are performed while the revolution speed of the disc motor and the filtering characteristics of a focus servo and a tracking servo are changed.
When all kinds of servo control are stopped, the system controller 424 outputs a signal to the clock output unit 423 to stop the supply of clocks to the DSP 412. The DSP 412 goes into a sleep mode to reduce power consumption.
During debugging in the development of the optical disc device 400 or the repair of the optical disc device, in order to observe whether or not focus servo control or tracking servo control is correctly performed, the DSP 412 outputs the focus error signal or the tracking error signal to a serial port 425 according to an instruction of the system controller 424. The output of the serial port 425 is serial-parallel converted by using an instrument 426, which is connected to the optical disc device 400 and is provided only for the optical disc device. The data having been parallel converted is D/A converted by the instrument 426 and is outputted as an analog signal. The analog signal outputted from the instrument 426 is observed by using an oscilloscope 427, so that the focus error signal and the tracking error signal can be observed.
In recent years, as computers increase in computing speed, higher-speed recording and reproduction are demanded from optical disc devices, which are the peripheral devices of the computers. Further, to increase the lives of batteries, lower power consumption is demanded from portable electronic equipment such as a laptop PC, a PDA, a video game machine, and a portable player that have optical disc devices.
Further, efficiency is demanded in development and repair after the shipment of products.
However, according to conventional optical disc devices, low power consumption meeting the above demands is not achieved and a control signal cannot be observed without a special instrument in development and repair after the shipment of products.
An object of the present invention is to provide an optical disc device which can solve the above problems and perform recording and reproduction at high speed with low power consumption. Another object of the present invention is to provide an optical disc device permitting a control signal to be observed with ease in development and repair after the shipment of products.